This invention relates to differential pressure transducers, and more particularly to differential pressure transducers in which a pair of pressure sensitive diaphragm assemblies are constrained to flex in unison when subjected to a pressure differential the magnitude of which is to be measured.
Various differential pressure transducers are known in which a rod or other rigid structure connects a pair of pressure sensitive diaphragms and causes the diaphragms to flex in unison. When one of the two pressures forming the differential is applied to one of the diaphragms and the other pressure is applied to the other diaphragm, the diaphragms flex toward the lower pressure. As the magnitude of flexing can be correlated with the magnitude of the pressure differential, the latter quantity is obtained by measuring the distance through which the diaphragms move.
In one type of transducer, described in U.S. Pat. No. 3,882,443 to S. Mortia, dated May 6, 1975, a permeable core is attached to a rod which separates the diaphragms. A pair of electrical coils are disposed on each side of the core to form an inductance circuit. Movement of the core when the diaphgrams flex in response to a change in pressure differential alters the inductance of the circuit, thereby affording a method of measuring the new pressure differential.
Another approach that avoids extensive electric circuitry within the transducer is illustrated in U.S. Pat. No. 3,901,082 to L. Lyon, dated Aug. 26, 1975. In this patent a post is used to rigidly separate the diaphragms, and also deflects a leaf spring cantilever beam having strain gages mounted thereon when a differential pressure is applied to the diaphragms. The actual connection between the post and beams is accomplished by a metal stamping which is clamped to a flange on the post, the stamping having a tab which is brazed or otherwise fixed over its entire area to an end portion of the beam. While this approach has the advantage of relative simplicity of construction, it is still subject to improvement. The natural tendency of the cantilever beam when deflected is to move in an arc, but the fixed connection between the end of the beam and the metal stamping causes the end of the beam to move instead in a straight line path transverse to the unflexed beam plane. This in turn places an unnecessary stress on the beam and produces a large variation in the strain level at different points along the beam, making the location of the strain gage critical. Calibration problems can result if the gages are placed at locations where the beam strain is considerably more than would be the case if the beam was permitted to flex naturally, while placing the gages at a low strain location prevents efficient utilization of their full range.